1. Field of the Invention
The present invention relates to the treatment of municipal solid waste (MSW) and sludge by microorganisms.
2. The Prior Art
Governmental efforts have failed to solve the growing problem of sewage sludge pollution which is becoming a serious threat to our already endangered soil resources. This has resulted from strong government promotion of large-scale land disposal of 15 to 40 tons per acre of inadequately modified sewage sludge.
The harmful effects of this practice on soil structure, such as allowing toxic metal accumulations and leachate into the underlying water table, should be obvious. It is, in fact, as if the most basic of agricultural practices, proven over thousands of years, were being completely ignored.
One thousand years ago the fertilizing practices of the preceding 3,000 years were described in a manuscript by El Doctor Excellente Abu Zacharia Iahia of Seville, Spain. It was translated from Arabic into Spanish by order of King Carlos IV and published in 1802 as El Libro de Agricultura, followed by a French edition in 1864. Though not yet available in English, it has often been referred to and quoted for its undisputedly sound principles by English writers on agriculture.
The book describes the highly developed agricultures in China, India and Persia at about 1,000 year intervals. The last such development came some 1,000 years later during the Arab rule of Spain, when natural agriculture and horticulture no doubt reached its highest development ever with respect to yields, varieties, and quality of produce.
Of particular interest here is, of course, what Abu Zacharia, who was also the owner and operator of a large farm, writes on the composition, preparation and use of manures, the basic source for all fertilizers. Until recent times, the human variety of manure was the preferred source. By his own experience, confirmed by that of other farmers over thousands of years, he could stress in the strongest terms that manures should never be applied to the land alone or while fresh, but always be mixed with five to ten times as much plant waste, preferably including some animal bedding for its valuable urine.
This would not only provide a better balanced and more effective fertilizer, especially if left in a pile for a month or two for "mellowing," but also many times more of it. Much better still would be subjecting the mixture to composting, which he describes in great detail, including what the finished product should look like and how best to use it.
Just why manures should not be used alone was, of course, not known then. Today we know the reason very well, although it is still widely ignored, namely, that organic carbon is the basic nutrient for all forms of life, being about 50% of all living tissue. Food for man, beast and all other forms of life is therefore also about 50% carbon, of which most is utilized, and only a very small portion remains in the excrements after the digestive process. To what extent any such remaining carbon is affected by that process so as to be of little or no value for recycling to the soil to sustain its all-important microbial activities, which includes the natural soil process of composting, remains in controversy. But the obvious conclusion from what is known and factual is that applying manures or sewage sludge alone to the land will not improve it.
This will inevitably lead to more of the same kind of carbon deficiency or soil impoverishment that chemical fertilizers are creating in our times, which are commonly described as being poor in humus or organic matter, which is 50% carbon.
In their belated attempts to find a way to reduce the rapidly worsening sludge disposal problem, federal and state governments have in recent years funded large and costly plants for composting sewage sludge, thereby hoping to make it less objectionable for land and dump site disposal. The technology entails mixing the partly dehydrated sludge with about three times the volume of wood chips as a bulking agent. The mixture is then composted in large open piles during four to five weeks followed by curing in other piles for another three weeks. The resulting compost is then screened in order to recover as much as possible of the very hard-to-degrade wood chips for reuse as bulking agent with another batch of sludge.
The resulting product is therefore as deficient in carbon as is the sludge. It is certainly not compost. Because there has not been enough carbon for the necessary microbial activities, this final material is essentially sewage sludge as to consistency and structure with high leachability into the underlying water table. Worse, it still has the same high content of highly toxic metals as the original sludge.
Another serious and environmental problem from such alleged "composting" is the polluting leachate and the foul air from the piles. This is aggravated as compressed fresh air is forced through the piles, because such air is toxic to the microbes and stops their activities until aeration ceases, causing condensation of the moisture to lodge on the surface or bottom of the pile, depending upon air being drawn out of the pile or blown into it.
The reason for the carbon deficiency is that wood chips, like all wood, contain a great deal of lignin, nature's own very efficient preservative which gives wood its high resistance to decay.
The high temperatures developed by the microbial activities in an efficient composting process, which is more than adequate to destroy all the pathogens which abound in sewage sludge, can obviously not be attained by the above method. Minimum temperature requirements were established by the federal EPA about 20 years ago much along the lines already established in European countries. They are brief in that sludge and garbage pathogens are destroyed by composting within 20 to 30 minutes at temperatures of 140.degree. to 160.degree. F. To accommodate its method, EPA's temperature requirements have had to be lowered to 131.degree. F., and the time extended to a full three days. No efficient industrial-type composting method can meet such requirements except by doubling or tripling the processing time, although it will much more than meet the original higher requirements for pathogen destruction.
The absurdity of the situation is spotlighted by the fact that the method for which the new EPA rules were tailored cannot actually meet them. While the modest temperature of 131.degree. F. can be attained, it cannot remain more than a few hours, or until the pile has to be aerated, which happens six to eight times every 24 hours with compressed air through a complicated system of perforated pipes. This, of course, brings down the temperature in the pile to near ambient levels, putting a full stop to the microbial activities, from which it will take a few hours to recover. Actual exposure to 131.degree. F. is therefore unlikely to be more than half of the stipulated three days. Beside that, the temperatures can never be uniform in stationary piles, and never much over ambient on their surface, with good chances for any pathogens to survive.
The first large government composting operation for sewage sludge was located at Beltsville, Md. Generously funded by various government authorities, operations began in the early 1970s and continued until 1978. In 1974, it was announced that a successful windrow method utilizing wood chips as bulking and moisture-absorbing agent had been developed. Upon inspecting the operations, there was strong evidence of bad odor and leachate problems. A fully enclosed composting method might solve these problems, but most of the wood chips would break down and be composted, and therefore not used again. That would not do at all, as it would be too expensive.
Despite the setbacks by several closed down operations, promotion of the EPA method continues unabated, now also by states and universities inspired by EPA's official evaluation of its own contribution, which reads as follows: The new Beltsville composting process represents a major advance over previously known composting methods.
Several other attempts have been made in the past to solve these prior art problems, and prior proposals include the following.
Eweson U.S. Pat. No. 3,138,447 discloses a multistage process for producing organic fertilizer.
Larson U.S. Pat. No. 3,178,267 discloses an automatic control of a digester for converting inorganic material into plant food.
Eweson U.S. Pat. No. 3,235,369 discloses a fermented fertilizer having a granular structure.
Eweson U.S. Pat. No. 3,245,759 discloses an apparatus for making organic fertilizer.
Yeagley U.S. Pat. No. 4,499,614 discloses an organic waste bioconverter.
Kimura U.S. Pat. No. 5,071,462 discloses producing organic fertilizer with the use of nitrogen fixing bacillus.
Johnson U.S. Pat. No. 5,139,554 discloses a composting method using inclined vessel.